<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<p id="one">
    <span>这是一个段落</span>
    <span>333333</span>
</p>
<script>
    let obj = document.getElementById('one');
    console.log(obj.innerHTML);                  //<span>这是一个段落</span>
    obj.innerHTML = '<span>hello world!</span>';
</script>
</body>
</html>